The present invention relates to an amorphous semiconductive surface coating for a surfical implant, and more particularly, it relates to methods of making such surface coatings.
Surgical and, in particular, cardiovascular implants must be highly compatible with blood in order to reduce the risk of valve occlusions by thrombus, thromboembolism and anti-coagulant-related hemorrhage. It is known that for antithrombogenity it is necessary to have a low peak-to-valley height (roughness) in order to prevent the deposition and destruction of corpuscular components of the blood and the activation of the coagulation system connected therewith. Further, it is also known that direct charge exchanges between coagulation-specific proteins and the implant surface must also be prevented.
Because of its excellent surface finish, pyrolytic carbon was at first used as a cardiovascular implant material but the hemocompatibility of this material was less than desired, because of the electronic structure of the surface. A transfer of electrons as a result of tunneling of occupied, valence band-like states of the blood protein into free states of the solid leads to a splitting of the fibrinogen in the blood. The thus-resulting fibrin monomers may then polymerize and lead to an irreversible thrombus.
A doped, semiconducting rutile ceramic with a higher hemocompatibility than pyrolytic carbon was then used but technological problems related to the surface roughness of this material made the manufacturing costs prohibitive.
It is already known to coat surgical and in particular cardiovascular implants with an amorphous semiconductive thin film. Coating has the advantage that the substrate material need only meet the demand for mechanical stability, whereas the antithrombogenic requirements are fulfilled by the amorphous semiconductive surface layer.